String constants not protected

I've spent a few hours messing with this and I'm just stuck. Sorry if I'm being dense.

I'm running the interactive version and decompiling to monitor the results and it's just not behaving as I assumed it would. My string constants are not being obfuscated, no matter what I try.

I created one global rule of "normal". Everything get obfuscated but the strings. I added a protected for constants. No difference. I can't figure out how to override the constant's advanced properties that are documented to experiment with that.
The UI only lets me add that protection as-is.

Ultimately I need for this to run on a build server, so I can't use a project file that I know of because I need to specify the input/output at runtime.

I'm willing to instrument the source with attributes if that's what's needed but couldn't figure that out either.